Find all nodes that have an attribute that matches a certain value with scala

Question

I saw the following example on Nabble, where the goal was to return all nodes that contain an attribute with an id of X that contains a value Y:

//find all nodes with an attribute "class" that contains the value "test" val xml = XML.loadString( """<div> <span class="test">hello</span> <div class="test"><p>hello</p></div> </div>""" ) def attributeEquals(name: String, value: String)(node: Node) = { node.attribute(name).filter(_==value).isDefined } val testResults = (xml \\ "_").filter(attributeEquals("class","test")) //prints: ArrayBuffer( //<span class="test">hello</span>, //<div class="test"><p>hello</p></div> //) println("testResults: " + testResults )

As an extension to this how would one do the following: Find all nodes that contain any attribute that contains a value of Y:

//find all nodes with any attribute that contains the value "test" val xml = XML.loadString( """<div> <span class="test">hello</span> <div id="test"><p>hello</p></div> <random any="test"/></div>""" ) //should return: ArrayBuffer( //<span class="test">hello</span>, //<div id="test"><p>hello</p></div>, //<random any="test"/> )

I was thinking I could use a _ like so:

val testResults = (xml \\ "_").filter(attributeEquals("_","test"))

But it doesn't work. I know I can use pattern matching, but just wanted to see if I could do some magic with the filtering.

Cheers - Ed

I found Xpath language is simpler github.com/nrinaudo/kantan.xpath and is compile time safe in Scala — WeiChing 林煒清
– WeiChing 林煒清, Commented Jan 17, 2018 at 4:20

Daniel C. Sobral · Accepted Answer · 2012-02-12 17:44:58Z

First, XML are literals in Scala, so:

val xml = <div><span class="test">hello</span><div class="test"><p>hello</p></div></div>

Now, as to the problem:

def attributeValueEquals(value: String)(node: Node) = { node.attributes.exists(_.value.text == value) }

In fact, I'd have used "exists" instead of "filter" and "defined" for the original problem as well.

Finally, I personally prefer operator style syntax, particularly when you have a ready function, instead of an anonymous one, to pass to "filter":

val testResults = xml \\ "_" filter attributeValueEquals("test")

The original mixes operator style for "\\" and dot style for "filter", which ends up quite ugly.

if you are using scala 2.9.1, please see this answer stackoverflow.com/questions/3819485/… (this selected answer returns a NodeSeq() on 2.9.1

Dmitry Stropalov · Accepted Answer · 2010-10-30 18:02:04Z

Code snippet in the question doesn't working with Scala 2.8 - due to this comparasion

(_ == value)

Needs to be replaced with (_.text == value) or (_ == Text(value)) or change type of value from String to Text.

And in Daniel's answer (_.value == value) needs to be replaced with (_.value.text == value).

Peter O. · Accepted Answer · 2011-12-10 19:53:51Z

The previous solutions didn't work for me because they all look for any value that matches. If you want to look for a particular attribute with a value, here is my solution:

def getByAtt(e: Elem, att: String, value: String) = { def filterAtribute(node: Node, att: String, value: String) = (node \ ("@" + att)).text == value e \\ "_" filter { n=> filterAtribute(n, att, value)} }

And then

getByAtt(xml, "class", "test")

This will differentiate between class="test" and "notclass="test"

Maxime · Accepted Answer · 2009-09-25 13:59:57Z

I'm quite new to Scala, I propose you this solution, but I'm not sure this is the best one:

def attributeValueEquals(value: String)(node: Node) = { node.attributes.foldLeft(false)((a : Boolean, x : MetaData) => a | (x.value == value)) } val testResults = (xml \\ "_").filter(attributeValueEquals("test")) println("testResults: " + testResults ) // prints: testResults: ArrayBuffer(<span class="test">hello</span>, // <div id="test"><p>hello</p></div>, // <random any="test"></random>)

Germán · Accepted Answer · 2009-09-25 14:22:31Z

0

def nodeHasValue(node:Node,value:String) = node.attributes.value != null && node.attributes.value.contains(value) (x \\ "_").filter( nodeHasValue(_,"test"))

answered Sep 25, 2009 at 14:22

Germán

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2 Comments

Germán Over a year ago

I would suggest maxme's answer for the currying, but my answer for the use of 'contains' rather than a fold. Combine them!

Germán Over a year ago

Well, Daniel's answer beats both. Kudos.

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